The invention relates to an intake manifold with an integrated exhaust gas recirculation system, which has a connection for the exhaust gas and inlet openings for the various intake channels.
Intake manifolds of this general type are known in the art. For example, WO 97/34081 discloses an intake manifold in which channels for exhaust gas recirculation are formed by grooves in the cylinder head flange. Once the intake manifold is mounted to the cylinder head, the cylinder head forms the missing wall of the exhaust gas recirculation channels.
Due to the thermal stresses that occur in the exhaust gas recirculation channels, at least the cylinder head flange of the intake manifold must be made of a heat-resistant material. This is a minor requirement in intake manifolds made of metal. But in intake manifolds made of synthetic resin or plastic material, which are a particularly cost-effective solution, the thermal stresses occurring in the exhaust gas recirculation system may cause damage.
To keep the thermal stresses in the synthetic resin intake manifold low, German patent application no. DE 198 19 123 A1 proposes to accommodate the exhaust gas recirculation system in a heat-resistant intermediate flange, which connects the cylinder head flange of the intake manifold with the cylinder head itself. This solution, however, implies a complex structure of the intake tract. The cost savings achieved by making the intake manifold of synthetic resin are reduced by the additional cost of the intermediate flange.
Thus, it is the object of the invention to provide an intake manifold with an integrated exhaust gas recirculation system, in which the thermal stress of the intake manifold due to exhaust gas recirculation is low.
This and other objects are achieved by the invention as described and claimed hereinafter.
The intake manifold according to the invention has the known structure comprising inlet, plenum, intake channels from the plenum, and outlets to the cylinders. The outlets may advantageously be formed as a cylinder head flange. The intake manifold may be designed for an in-line or V-type arrangement or any other type of arrangement of the cylinders. It is also possible to provide several plenums, which are assigned to corresponding groups of intake channels.
The intake manifold further has a connection for the exhaust gas recirculation system. Via an exhaust line, the exhaust is directed to inlet openings, which are arranged, respectively, within the flow region of the intake air influenced by the intake channels. This makes it possible to supply each cylinder separately with exhaust gas to ensure a desirable, particularly homogenous distribution of the exhaust gas over all cylinders. In the exhaust gas supply region, valves may be provided to permit a cylinder-selective introduction of the exhaust gas as a function of the cycle of the individual cylinders. The flow region influenced by the intake channels should be understood to mean the region that permits the supplied exhaust gas to a large extent to be assigned to an particular intake channel. Thus it refers to more than just the volume of the intake channel itself. The inlet openings can also be arranged within the volume of the plenum and in the proximity of the intake openings formed by the intake channels, which open out into the plenum. This essentially permits a clear assignment of the exhaust gas to the individual intake channels. As an alternative, however, a stoichiometric distribution of openings in the exhaust line is also possible. These openings achieve a uniform distribution of the exhaust gas in the intake air, which is subsequently supplied to the intake channels.
Particularly if there are several plenums, a plurality of connections and exhaust lines may be provided in the intake manifold. In the design of the intake manifold, the connections and the exhaust line advantageously provide some design latitude because fewer boundary conditions due to other components (e.g. injection valves, cylinder head cover, generators, pumps, fuel strips or clearances for screws) have to be taken into account when running the lines within the plenum. A further advantage is that the intake air flows around the exhaust line within the plenum. This makes it possible to cool the exhaust gas before it is introduced into the intake manifold. Cooling, however, does not need to be achieved by a separate channel system or a cooling medium that differs from the combustion air. Cooling therefore does not involve additional design complexity. Moreover, the tightness requirements of the exhaust gas duct in the intake manifold are lower since minor leaks merely cause earlier mixing of the exhaust gas with the intake air.
Ensuring a clearance between the exhaust line and the walls of the intake manifold prevents heat conduction between the exhaust line, which gets hot, and the material of the intake manifold. This greatly reduces the thermal stress of the intake manifold. Direct heat conduction is possible only via the fastening means or mounting members, which fix the exhaust line within the interior of the manifold. The mounting members used comprise at least one seal, which is required at the rim of a passage for the connection. The connection is thus located outside the intake manifold permitting a connection to the exhaust gas system of the internal combustion engine. Further mounting members for the exhaust line may include any of the means available in fastener technology. Feasible, for example, are screwed and riveted connections, as well as clamped, plug-in and snap-in connections. If the intake manifold has a multi-shell structure, the exhaust line may be fixed through the assembly of the shells of the intake manifold. Bars as spacers can minimize heat conduction with sufficient fixation. Further minimization is advantageously possible if the mounting members themselves do not conduct heat well. This can be achieved, in particular, by a small cross-section of the fastening means, which create a heat bridge between the intake manifold wall and the exhaust line, or by selecting materials with low thermal conductivity, e.g. ceramics.
In accordance with one particular embodiment of the invention, the fastening means used may also be the exhaust gas inlet openings of the exhaust line if they have to be run through the walls of the intake channels. This necessarily results in a connection between the exhaust line and the walls of the intake manifold, particularly the intake channels, by means of which the exhaust line can be fixed in position.
Such an arrangement of the inlet opening, which results in a defined exhaust gas admission into the intake air within the intake channels, can be improved by an advantageous design of the junction in the passages of the wall. For example, a bellows-form tube section may be used, which on the one hand, due to the enlarged surface of the bellows or the extension of the heat conduction path, results in thermal insulation of the exhaust line with respect to the intake manifold. The bellows-form tube section itself is suitable for transferring the exhaust gas and introducing it into the intake port. Furthermore, due to its elasticity, the bellows allows for a certain compensation of tolerances between the exhaust line and the intake manifold. This compensation is necessary because of the different thermal expansion of the materials of the exhaust line and the intake manifold and because of the different thermal stresses to which they are subjected. Instead of the tube section, a ceramic fitting may be used to ensure thermal insulation at least between the exhaust line and the intake manifold. The ceramic fitting furthermore permits any geometry of the inlet point, e.g. in the form of a nozzle. The geometry of the inlet point can then be designed to ensure optimal distribution of the exhaust gas within the intake air.
If the inlet openings, as mentioned above, are arranged in the region of the intake openings of the intake channels, heat conduction can be further reduced. It also permits a central inlet in relation to the cross section of the intake channels to ensure uniform distribution of the exhaust gas within the intake air. It moreover allows for large tolerances.
One advantageous embodiment of the exhaust line results if said line has a multi-shell construction. The shells may for instance consist of two deep-drawn metal parts, thereby permitting the realization of complex geometric structures of the exhaust line. In addition, further functional components may be integrated in the shells. Particularly flanges or spacers to fix the exhaust line within the interior of the intake manifold may be cost-effectively produced. The duct structure formed by the shells may be supplemented by further components that are mounted to the basic part. It is possible, for instance, to complete the exhaust line by connecting pipes to it.
Producing the exhaust line from a metallic material ensures good heat conduction from the exhaust to the intake air within the intake manifold. This allows for optimal cooling of the exhaust gas up to the inlet points, so that the walls of the intake manifold are subject to less thermal stress in the region of the inlet points. Metallic materials are furthermore highly heat-resistant and thus allow high recirculation rates of exhaust gas into the intake manifold. If thermal stress is low, a heat-resistant synthetic resinl, e.g. PPS, may be used for the exhaust line. This lowers the costs of fabrication and materials.
The intake manifold itself is advantageously made of synthetic resin maaterial. This permits cost-effective manufacture. Particularly when using multi-shell techniques, the exhaust line may be readily integrated into the intake manifold prior to final assembly of the intake manifold. Integration is also feasible, however, in synthetic resin intake manifolds produced by meltable core techniques. In this case, either an installation opening for the exhaust line has to be provided or the exhaust line has to be cast into the core in order to define its position within the interior of the intake manifold. The invention may of course also be used in intake manifolds that are made of metal, e.g. aluminum.
Advantageously, the geometry of the exhaust line within the intake manifold may be designed in such a way that the path traveled by the exhaust gas from the respective connection to the respective inlet opening to the intake channels is always the same length. This synchronizes the dead times that occur between the opening of the exhaust gas recirculation valve and the inflow of the exhaust gas into the intake channels. It furthermore achieves uniform cooling of the exhaust gas up to the individual inlet points. The combination of these effects optimizes pollutant reduction through exhaust gas recirculation. Furthermore, a possible reduction in engine torque, which could occur due to a short caused by the exhaust lines, is prevented. The length of the lines counteracts this in the form of a throttle.
These and other features of preferred further developments of the invention are indicated in the claims as well as in the description and the drawings. The individual features may be implemented alone or in various sub-combinations in embodiments of the invention as well as in other fields and may constitute advantageous and protectable embodiments per se, for which protection is hereby claimed.